Simplify libmadx.get_table return signature
Merge branch 'remote-exception-traceback' into simplify-libmadx-gettable
Fix str.split in libmadx._split_header_line

str.split expects the 'maxsplit' parameter as its *second* *non-keyword*
argument.
Fix regression: table name needs to be encoded

On python3 str and bytes are different objects and we need bytes to
communicate with the C API.
Return only the table name from libmadx.get_twiss
Return Expression objects if possible

NOTE: this makes the returned types the columns in `libmadx.get_beam()`
more unpredictable which may be a bad idea.

It means, that you can not safely write implicit code like this any more:

    2 * seq.beam['ex']

But rather:

    2 * float(seq.beam['ex'])

And you will get the expression string via:

    str(seq.beam['ex'])
Merge branch 'simplify-libmadx-gettable' into active-sequence

Conflicts:
	src/cern/cpymad/libmadx.pyx
Add function libmadx.get_table_columns